1. Field of the Invention:
The present invention relates to a process for the recovery of aromatic nitrogen-containing compounds from an oily substance. More particularly, the present invention relates to a process for the recovery of aromatic nitrogen-containing compounds such as indole and the like aromatic amines from an oily substance such as coal tar by extracting the oily substance with a specific solvent.
2. Description of the Prior Art:
From the past, coal tar and residual oils obtained in thermal cracking of petroleum are known to be an oily substance containing aromatic nitrogen-containing compounds such as indole, quinoline and the like heterocyclic tertiary bases. Thus, various methods have been proposed hitherto as a means for separating such aromatic nitrogen-containing compounds from the oily substances. A typical method includes the steps of bringing an oily substance containing such aromatic nitrogen-containing compounds such as indole into contact with an acid to form a salt, for example, an oligmer salt in case of indole, and then subjecting the oligomer salt to thermal decomposition (Japanese Patent Appln. No. Sho. 62-249967). Another typical method comprises reacting indole in an oily substance with a caustic alkali to separate the indole as an alakaline salt thereof from the oily substance and then hydrolyzing the salt to convert it into indole ("Coal tar" Vol. 3, PP.189-194). However, these prior art methods wherein the aromatic nitrogen-containing compounds are first converted into salt form for separating them from the oily substance and the salts are then reconverted into the original compounds have drawbacks in that the steps and operations for the recovery of the compounds are complicated and the cost thereof is rather high.
Aromatic nitrogen-containing compounds such as indole, quinoline, isoquinoline, acridine, pyridine, picoline, lutidine and collidine are important as solvents or starting materials for producing medicines, agricultural agents and other type industrial products. In general, however, coal tar and the like oily substances are low in such aromatic nitrogen-containing compounds. Thus, the processes for recovering the compounds involve difficult operations which make these prior art methods economically unattractive.
Under the circumstances above mentioned, there is a great demand for developing a new method for the recovery of such useful aromatic nitrogen-containing compounds in an efficient manner from an oily substance lean in such compounds.